Toughness Feat Question

[Darth That Guy]

I am having a hard time understanding how the Toughness feat works and all in Pathfinder. The definition of it below is confusing for a noob like me.

You have enhanced physical stamina.

Benefit: You gain +3 hit points. For every Hit Die you possess beyond 3, you gain an additional +1 hit point. If you have more than 3 Hit Dice, you gain +1 hit points whenever you gain a Hit Die (such as when you gain a level).

So, for example, let's say I am a Human Fighter at level one and I take my d10 plus Con mod of let's say 3... that would give me a base HP of 13. Now I select the Human feat of "Toughness" indicated above. Of course the +3 is a no brainer and my HP increases to 16, but the rest I am lost on. I saw on another post that Hit Die is basically just same as saying your level. So does that mean that with toughness I gain +1 HP after every three levels, on top of the d10 (or half) plus Con mod of 3 that I will be doing each level?

Going by what I just wrote, what would my HP total be by level 5, going by half of d10?

[Chess Pwn]

Toughness works like this
HOW MUCH YOU ADD TO YOUR HP
lv1 (roll + con) +3
lv2 (roll + con)
lv3 (roll + con)
lv4 (roll + con) +1
lv5 (roll + con) +1
lv6 (roll + con) +1
...

So at lv20 it will be giving a +20 total to your MAX HP.

Also think, it's giving as much HP as your level. Except the first three get their bonus all on lv 1.

So your example question.
Lv1 hp=16 (10+con+3)
Lv2 hp=16+8.5=24 (5.5+con)
Lv3 hp=24+8.5=33 (5.5+con)
Lv4 hp=33+9.5=42 (5.5+con+1)
Lv5 hp=42+9.5=52 (5.5+con+1)
52

[Nefreet]

Chess Pwn is correct.

It's designed to give 1st level PCs a bigger benefit than just "+1 HP per Hit Die".

[Ciaran Barnes]

You get one extra hit point per hit die / level that you have. However, you get a minimum of three extra hit points.

[Lifat]

You could choose to think of the toughness feat like this:

+1 hit point per level, minimum +3.

[Wheldrake]

And don't forget your favored class bonus. For most PCs, this means you get another additional +1 hit points per level (*and +1 skill points, if you're human).

Yes, you have many other options, but the hit point is usually the best choice.